Hydrodynamic brake system



July 4, 1961 H. w. cHRlsTENsoN ETAL 2,990,919

HYDRODYNAMIC BRAKE SYSTEM Original Filed Deo. 28, 1955 2 Sheets-Sheet 1 wmwl NSW

o Inventors Attorney July 4, 1961 H. w. cHRlsTENsoN ET A1. 2,990,919

HYDRODYNAMIC BRAKE SYSTEM Original Filed Dec. 28, 1955 1 2 Sheets-Sheet 2 Inventors Hovafii//S speeds.

United States Patent O 2,990,919 HYDRODYNAMIC BRAKE SYSTEM Howard W. 'Christenson and Robert M. Tuck,y Indianapolis, and Keith A. Bailey, Speedway City, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware -Original application Dec. 28, 1955, Ser. No. 555,847, now

Patent No. 2,864,473, dated- Dec. 16, 1958. Divided and this application Mar. 31, 1958, Ser. No. 725,396

28 Claims. (Cl. 18S-90) v This invention relates to a transmission having a hydrodynamic brake and control system and more particularly a loop circuit control system for a hydrodynamic brake. This application is a division of the applicants `application ,S.N. 555,847, filed December. 28, 1955, and now Patent The hydrodynamic brake may be employed in a trans-1 'I `mission including a hydrokinetic torque converter having a iluid supply. system providing a volume of uid proportional to speed. The exhaustfrom the torque converter may then be used as the fluid supply for the brake. When the brake is supplied with fluid, the brake absorbs torque,

and the uid is ejected under pressure through a hydraulic loop circuit having manual and automatic valves to con- Itrol the brake capacity and a restriction provided by a cooler and returned to lthe brake chamber. Fluid is conthe loop circuit to control the brake capacity. The maximum brake capacity in the full brake range, which increases with brake speed, is obtained when the brake chamber is full and the pressure in the chamber is controlled by a regulator valve located between the restric `tion and the brake inlet which is closed to fill the brake 'chamber and opened by pressure inthe brake inlet line to limit the pressure in the full Ibrake chamber. The

maximum brake capacity in the limited brake range,l

which is a constant value, is obtained by a torque limiter or relief valve located between vthe restriction and the brake outlet which limits the pressure in the brake chamber and the brake capacity toa constant safe value at yall The manual valve controls the size of an orifice to control the release of iiuid from the loop circuit at a point between-the restriction and the brake outlet to partially evacuate thebrake chamber to provide partial brake capacity which may increase with speed -to the `limited .maximum brake capacity. Though the brakel capacity varies-with speed, the same size orifice will provide the same brake capacity for a given speed because the system is stable, since a change in brake capacity will change the amount of duid released to counteract the change in brake capacity.

The manual cont-rol valve in the bra-ke ofE position" -evacuates the brake and permits the converter exhaust `to continue to ow throu-gh the cooler.

The regulator valve is closed to-ll the brake chamber and may open to limit the pressure in the brake chamber when .full to Iprovide the maximum brake capacity in the full brake` range `and also controls the pressure in the converter chamber.

An object of the invention is to provide a stable control for -a hydrodynamic brake wherein iiuid is constantly added and released from the brake circuit to maintain the desired braking effect.

Another object of the invention is to provide in a cir- I' cuit fora hydrodynamic brake, a supply of Huid for the circuit and manually set automatic controls to maintain the braking effect and automatic means to limit the maximum braking eifect.

Another object of the invention `is to provide in combination, a torque converter and hydrodynamic brake, a control system for the hydrodynamic brake :vlrereinthe .tinuously supplied to the loop circuit and is released from to the brake outlet line 61 which is connected through the y check valve 63 to cooler inlet line 62.

2,990,919 Patented July 4, 1961 ICC torque converter outlet fluid is employed as a source .of supply for the brake control system.

Another object of the invention is to provide in combination, a cooling system and a hydrodynamic brake control system employing the same fluid supply and cooler.

These and other objects and advantages of the invention will be apparent from the following description and drawing of the preferred embodiments of the invention.

FIG. l is a diagrammatic view of a torque converter .and a hydrodynamic brake with a control circuit having a rotary control valve.

FIG. 2 is a View showing characteristic curves for these hydrodynamic -brakes and control systems. j, j l V FIG. 3 is a similar diagrammatic view with a control circuit having a reciprocating control valve. Y The transmission 10 has a torque converter unit 11 an .a hydrodynamic `brake unit 12 mounted in the transmis- Vsion housing' 14. The transmission is driven from an enk18 and a rear wall which extends inwardly to ground vsleeve 29 where itis secured to the pump drive sleeve 27 carrying the pump drive gear 28 which are rotatably supported on ground sleeve 29. The impeller 26 has an annular series of impeller blades 31. The bladed turbine 32 is mounted on hub 33 fixed on converter output shaft 34. The stators 36 and 37 eachv having torque reaction blades -are mounted yby one-way overrunning clutch devices 38 von the ground sleeve 29 which is fixed to the housing 14.

The impeller 31, turbine 32 and stators 36 and 37 provide a conventional torque converter having a converter chamber The output shaft 34 is keyed to the hydrodynamic brake rotor 41 having an annular series of impeller vanes '42 l which rotate in brake chamber 40 between the fixed vanes 43 and 44 which are mounted on the transmission housing 14 and projecting into chamber 40. The output shaft 34 is supported at the rear of transmission -housing 14 by the bearing -47 `and at the forward end by arbearing 48 lmounted in the flywheel 18.

The brake control system is supplied with uid, usually oil, from a sump 50 having a vent 51 connected by purrip inlet line 52 to the positive displacement pump 53 which `is driven by gear 28 to supply lluid to the lconverter feed line 54. I-f the pump has `a relief Valve, it is set to relieve at -a high pressure so the converter pressure is controlled, 55

thus acts only as a safety valve. The iiuid leaves the -conas explained below, by pressure regulator valve 82 and verter through converter outlet line S6 which may have a ylilter 57 and a one-way valve 58.' The hydrodynamic brake rotor 42 acting as a. centrifugal pump, pumps iluid out of the chamber 40 yand into a tangential port leading The converter outlet line 56 is also connected to the cooler inlet line- 62 which is connected to the cooler 66 which not onlyfunctions to cool the fluid but to provide a restriction in the :brake loop circuit. 'Ihe outlet of cooler 66 is connected tothe cooler outlet line 67 and brake inlet line 68 which returns the uid via passage 77 to bra-ke chamber 40.

The system is manually controlled by a rotary valve 70 having a cylindrical housing 71 and a rotary valve having three' land portions illustrated in sectional views Vatg7.3, and 8.6.i11 the brake on position. @Movement of the valve 70 in a clockwise direction, 90 degrees, places the valve in the brake oit position. The brake outlet line 61 has a branch line 69 which is connected to the manually controlled valve 70 and in the brake on position 'blocked by brake outlet control land 73. When the valve 70 is in the brake otr' position, line 69 is connected by the sump line 74 and main sump line 76 to sump 50 to drain brake chamber 40 to release the brake. The land 73 has a slot 73 having substantially the same circumferential dimension as the cooperating port 71' for line 74. 'The axial dimension of the slot is narrower than the port 71 so that as the valve moves from the brake full on or Wide open position, a gradually decreasing orifice is provided until in the brake off position the valve is closed stopping flow between lines 69 anl "74. A parallel branch of the line 69 is connected to torque limiter valve 79 which will relieve excessive pressure in the brake outlet line to limit the pressure and maximum braking elfect or torque capacity to a safe value and by-pass the fluid through line 74 and line 76 to the sump 50. The cooler outlet line 67 is connected to the brake inlet port portion of the control valve 70 where land 75 in the brake on position illustrated connects line 67 through valve 70 to brake inlet line 68 and passage 77 to supply fluid to the brake chamber 40. The cooler outlet line 67 is connected by branch 81 to the pressure regulator or relief valve 82 to the main sump line 76 to permit ow of iluid from the converter through `the loop system to the sump when the land 75 is closed and limit the converter pressure. The valve 70 has a scavenge land 86 which in the brake on position illustrated which closes the air pressure supply line 87 having an orifice 88 and connects the brake vent line 89 through the valve to sump vent line 90 to the sump 50 to provide air communication between the brake and sump. In the brake off position land 86 blocks line 90 and connects air line 87 to brake vent line 89 to augment brake chamber scavenging.

Operation When the transmission is operating, pump 53 supplies fluid under pressure from sump 50 through the line 54 in relation to impeller shaft speed to keep the torque converter 11 filled so that the converter can hydrokinetically multlply or transmit torque to the output shaft 34. When the control valve 70 is rotated 90 degrees in a clockwise direction, it is in the brake off position, and the tluid from the converter tlows through line 56, cooler inlet line 62 where the check valve 63 prevents ow into the brake outlet line 61 toward the brake chamber. The fluid from the converter flows via lines 56 and 62 through the cooler 66 to the cooler outlet line 67 where it is blocked by the valve land 75. As the pressure rises in line 67, the regulator valve 82 opens releasing fluid in line 67 through branch 81, valve 82 and sump line 76 to sump t 50 to regulate the pressure in the converter. Due to the restriction of the cooler, the converter pressure will be higher than the pressure in line 81.

In the brake ott" position the brake outlet control land 73 of valve 70 is fully open and permits the brake chamber 40 to be exhausted via the brake outlet line 61, line 69 valve 70 and sump lines 74 and 76 to sump 50. If the sump 50 is located below or near the level of the brake chamber 40, the centrifugal action of the brake rotor 41 will be suicient to eject the fluid from the brake chamber 40 to sump 50 and the vent lines 89 and 90 will conduct air from the sump which is open to atmosphere to the brake chamber. Since the vent lines may be open at lall times when air scavenging is `not needed, land 86 is not needed. However, when the vehicle requires that the sump 50 be placed substantially above the level of the hydrodynamic brake 12, forced air scavenging is required to lift the iluid to completely evacuate the brake chamber to prevent drag. With the valve 70 in brake off position, the valve land 86 closes the vent line 90 extending to the sump 50 and conducts air from 4air supply line 87 through .line 89-to brake chamber 40. When the air scavenging system is employed, the air entering chamber 40 forces the fluid which is pumped by the brake rotor to the tangential port for line 61 through lines 61 and 69, valve land 73 and lines 74 and 76 to sump 50. The tangential port may be at the bottom of chamber 40 to aid complete evacuation. Any source of air under pressure may be used such as the -air brake supply. Since only a small quantity of air is required to scavenge the chamber, an orifice 88 restricts the air flow in line 87 to limit the drain on the source though the line is open when the brake is released.

When is it desired to fully engage the brake, the valve 70 is rotated to the brake on position to locate each of the three lands 73, 75 `and 86 as shown in FIG. 1. The land 86 closes the air inlet 87 to discontinue the scavenging of brake chamber 40 and connects vent line 89 past land 86 to drain line v90 and vented sump 50 to connect the center of brake chamber 40 to atmosphere to vent the air displaced by incoming fluid. The valve 70 at land 75 is opened and connects the cooler outlet line 67 to the brake inlet line 68 so that the converter exhaust ow via converter outlet line 56 is delivered to the brake chamber 40 to ll the hydrodynamic brake. Since the vehicle is normally coasting when the brake is applied, the positive drive pump will supply a volume of iluid substantially in proportion to brake speed va line 56 to the brake circuit. The lluid supply for these control systems should be substantially constant at a given speed but may vary with brake speed which will merely change the slope of the brake capacity curves but still provide stable control. The brake pumps fluid out of chamber 40 through a hydraulic loop circuit or through line 61, check'valve 63, line 62 where it joins the converter outlet ow, cooler 66, lines 67 and 68 and passage 77 and returns the iluid to the brake chamber 40. The check valve 63 prevents converter fluid flowing back via brake outlet line 61 to the brake chamber 40 and check valve 58 insures a positive pressure in the converter chamber to supply lubrication to the converter and any connected lubrication line. With the valve 70 in the full brake on position illustrated in FIG. l the valve 70 at land 73 completely closes the by-pass from brake outlet line 61 via branch 69 to the sump line 74. Under these conditions, the entire fluid supply from the converter outlet line 56 will enter the brake chamber until the maximum capacity for the brake speed is lattained as indicated by the maximum brake capacity curve, FIG. 2.

As the brake chamber is lled with uid, the brake capacity increases and the pressure in the hydraulic brake circuit increases. When thebrake chamber is full, the maximum brake capacity at any speed ywithin the full brake range from 0 to X (FIG. 2) speed is attained, as indicated by the maximum brake capacity curve. When the brake chamber 40 is full, there is a positive pressure in the inlet portion of the loop circuit between the restriction provided bythe cooler 66 and the brake chamber inlet or lines 67, 68 which is relieved by pressure regulator valve 82 since the regulator valve 82 is set to relieve at a pressure lower than the pressure at which torque limiter valve 79 relieves minus the pressure drop due to the restriction of the cooler 66. Thus the maximum brake capacity is main-tained in the full brake range by valve 82 which keeps the brake chamber full and limits the maximum pressure in the brake chamber by maintaining a constant pressure in line 67 when the brake chamber is full.

The brake torque increases with increasing vehicle speed and increasing volume of tluid in the brake chamber. Since the braking torque increases `as the second power of the speed, the brake capacity will increase rapidly at high speeds as shown in FIG. 2 by the dotted portion of the maximum brake capacity curve and the brake will generate a dangerous pressure or absorb more torque than the vehicle drive mechanism is designed to transmit. In order to avoid overloads, the maximum capacity of the brake vis limited to a safe value.

ASince the pressure in the brake outletportion of the loop circuit between the brake chamber outlet and the restricvtion'is a measure of the torque being absorbed by the hydrodynamic brake, the maximum capacity is limited to a safe maximum capacity in the limited brake range above X speed as indicated by the horizontal portion 96 of the maximum brake capacity curve by connecting the Ybrake outlet line -61 via branch -69 to the torque limiter valve 79 which limits pressure in the brake chamber to the desired safe maximum pressure to limit the torque capacity. When this pressure is exceeded, the 'valve 79 opens and drains uid vfrom` brake chamber 40 via lines 61 and 69, sump lines 74 and 76 to the sump 50 to partially evacuate the brake chamber and thus the braking by hunting the pressure in the brake outlet line 61.

The brake may also be manually controlled to vary Ythe braking eiect or to set the brake -for any partial braking effect. Between the full on position andthe full otf position of valve 70, the land 73 provides a variable orifice opening between the brake outlet portion of the loop circuit and the sump or lines 69 and 74 to provide partial braking. During partial braking operation land 75 connects line 67 to 68 to supply the brake and land 86 blocks air scavenge line 87 and connects vent lines 89 and 90. The pressure regulator valve 82 and the torque limiter valve 79 are closed. The converter outlet line 56 provides a supply of duid to the brake circuit which may be constant or vary with brake speed. When valve 70 is moved from the maximum brake position shown, .t

the land 73 rotates clockwise and the narrow slot 73 opens port 7-1 to provide a gradually increasing orice opening until at the end of the slot land 73 uncovers the full width of the port 71' in the brake oit position. As the oriice increases, the by-pass ow from the brake circuit at brake outlet line `61 via brauch 69, valve 70, lines 74 and 76 is increased. The partial capacity of the brake is manually determined by the size of the orifice at land 73 which automatically regulates the release of fluid evacuate the brake chamber to control the brake capacity. At a speed Y indicated by ordinate Y in thefull brake range from 0 to X speed, a partial oriii-ce opening will provide a certain brake capacity indicated at the-intersection of ordinate Y with the partial brake capacity f curve. A change in brake speed will provide a change in brake capacity as indicated by the partial brake curve. If the size of the orifice is increased, the brake capacity will be decreased and conversely if the size of the orifice `is decreased the brake capacity will be increased. If the speed varies the brake capacity will vary in accordance lwith a curve similar to the partial brake capacity curve.

`tl-"or any oriiice size of the land 73 a restriction is establised which in turn establishes a xed braking capacity lwhich is capable of producing, due to the pressure in the brake outlet, a tlow through the orifice equal to the ow of the uid supply to the brake loop circuit. Thus the orifice opening determines or maintains a certain brake capacity at a certain speed. The brake capacity increases with increasing speed in accordance with the characterisf In partial capacity operation above the full brake range,

for example, a speed Z in the limited brake range, a partial oriice opening would provide the brake capacity indicated at the intersection of the ordinate Z and the partial brake capacity curve. At this point the torque limiter from the hydraulic brake circuit to sump to partially '140 valve 79 opens to lmit/thebrake capacity tel the value' indicated by the flat rportion `96 ofthe maximum'brake capacity curve even though in` partial capacity operation, vthe .bra-ke chamber 40 is not full vthe vvalve 82 would not open. A reduction in speed would provide a brake capacity indicated by the partial brake capacity curve.

' Reciprocating v'alve control L `The transmission and hydrodynamic brake may also, be controlled to function in this manner by a control system having a reciprocating valve as illustrated in FIG. 3, The .transmission 10 which includes a hydrokinetic torque conlverter 11 and the hydrodynamic brake 12 is the same as described above and illustrated in FIG. l, with like reference numerals employed. j

, The control system illustrated in FIG. 3 has a sump y having a vent 151 from which uid is supplied by the pump inlet-line 152 tothe pump 153 lwhich supplies iluid .under pressure in accordance with engine speed to the .converter inlet line 154 which may have a filter, 15b to tillthe torque converter .11. The converter outlet is .connected to line 156 which may have a check valve With the `valve 171 in full on position, the-brake outlet iine 176, connects atangential port at theV outer perimeter Iof the brake chamber 40, to the annular port 177 located between the lands a and b adjacent the land a.v 'I'he converteroutlet linev156 is. connected to the annular port 178 located between the lands a and b adjacent the land b. The port 178 provides an annular passage which always .connects the converter outlet line 156 to cooler inlet line .181 which connects port 1=78 to cooler 182 which cools the uid and provides a restriction. The port 186 located between the-lands b and c adjacent the land b is connected by the brake inlet line 18f7 and passage 77 to brake ,Chamber 40. The port 191.1ocated between the lands b and c adjacent the land c is connected to cooler outlet line 192 .which is connected to the cooler 182. The cooler outlet line 192 is also connected by by-pass passage 193 having a pressure regulator valve 194 to the by-pass chamber 195. The valve 194, which always acts as a converter pressurefregulatingvalve and acts when lthe brake is f'ullmasl a Ibrake pressure regulating valve, is slidably mounted on guide rod 196 which is iixed in the valve body and extends across chamber 195. A coil spring 197 on rod 196 engages valve 194 -to hold the valve in closed position and abuts valve 211 at the other end. The by-pass chamber is always connected by .port-198 and line 199 to sump-150. A T-shaped exhaust port 201-b1ocked by land c of valve member 171 is connected by sump line 203 to the sump 150.l In the space between the lands a and b there is an aperture 20G-in the valve ,171 communicating with the axial bore 207 extending to the lower end ofvvalve 171 which connects -thespace be"- tween the llands ya and b to the chamber 208 in the valve body vbelow valve 171. The chamber 208 is connected 'by the torque limiter valve 211 which limits brake capacity to lay-passVVV chamber 195. 'I'he valve 211 is guided onthe rod 196 and retained in position by the spring 197 abutting valve'194. Brake ,chamber 40 y'is vented by -line 210 to vented sun'1p150.` l v Y 1 `f Operation v l I The operation of the reciprocating valve system of FIG. 3 is basically the same as the rotary valve system ,of FIG. l and the brake capacity is also in accordance Iwith thecurves in FIG. 2.' When .the transmission is :operating with the brake either onor olf, pump 153 suppliesfluid f romsump 150 under .pressure through the line 154 to the converter in relation to converter'inputlshaft spese When 'the Valve 17.1. is in the braise gif. position] the converter exhaust ows through line 156 around land bpf the valve 1171 to the cooler inlet line 181 without permitting How into valve bore 1712 and into the brake chamber. vThe fluid ows through the cooler 182 to the cooler outlet line 192 where the land c blocks entrance to the port 191 and fluid under pressure opens the regulator valve 194 regulating the pressure in the converter and flows through the by-,pass chamber 1-95 and annular port 1198 which is always open regardless of the position of land c through the sump line 199 to the sump 150. In the brake olf position, the brake chamber 40 is exhausted through brake outlet line 176, port 177, the space between the lands a and b, aperture 206, -axal bore 207, port 201, and line 203 to the sump 150. Thus the converter and brake chambers are connected by separate paths to the sump. The brake inlet line 187 is blocked at port 191 byland c.

When the valve 171 is moved to the brake full on position illustrated in FIG. 2, the brake outlet line 176 is `connected -to the port 177 where it joins the converter outlet vline 156 at Aport 178 vand both enter cooler inlet line y181 to ow through cooler 182. Since the output or brake shaft 34 is generally driving the input vshaft when the brake is applied, the converter acts as a coupling, andpump 153 andconverter output llow in line 156 is substantially proportional to brake speed. The torque limiter valve '211 opens at a pressure higher than the 4pressureat which the regulator valve 194 opens plus the pressure drop in cooler -182. Thus the pressure of oil inr the 2full brake chamber is limited in the full brake range or normal speed range from '0 to X speed by the vregulator valve 194 which will open in response to the higher brake inlet pressure created by the excess oil supplied from the source to permit excess oil 'to drain through chamber 195, port 198 and line 199 to sump 150 to keep the brake chamber full to provide the 'maximum brake capacity as shown by the sloped curve in FIG. 2 and limit `the pressure `in the brake chamber. The converter and brake outletlines 156 and 176 are connected through the space between the lands a and b, aperture 206 and the axial bore 207 to the chamber 208 at the lower end of valve bore 17.2. The pressure -of the Huid in chamber 208 is substantially the 'same as the pressure at the outer periphery of the brake, since the flow loss in the line 176 is low, and-this pressure acts upwardly on the valve member .171 so that the operator of the brake Awill feel a force resistinghis efforts to hold the valve in the brake full on :position or any other partial brake on position in proportion to the torque or braking effect of the brake. :If the brake tends to absorb more than the designed brake capacity at speeds above the normal range, the .pressure in the brake outlet line and chamber 208 will open torque limiting valve 211 and exhaust oil through chamber 195,` port 198, line 199 to sump 150. Thus excessive torque absorption by the brake is prevented above the full brake lrange or in the limited brake range, i.e., speed Z by the opening of valve 211 which reduces the pressure and the volume of oil in the brake chamber Vby removing oil from the brake circuit to provide a limited maximum brake capacity as indicated by the horizontal :portion 96 -ofthe maximum brake capacity curve in FIG. '2. Thus at any speed the maximum brake capacity is predetermined by the control system.

To provide `an intermediate or partial brake capacity, the valve 171 is `manually moved to a partial brake position between the brake full on .and oli positions so that the lower end of valve 171'w'ill partially uncover the axial -slot portion 202 of port .201 to provide a restricted orifice connecting chamber 208 to line 203 and sump 150. The orice is varied by moving the valve 171 betweenfull on .and olf positions in the same way as land -73.of.FIG. yl varies the orilice. In this way a part of the lluid is exhausted lfrom the brake circuit through the opening, the brake capacity'varies with speed as indicated `in FIG. 2 by the partial brake capacity curve, for example,

`opening Will increase the brake out .pressure and more uid will pass 'through the orice to sump to reduce the brake capacity to that partial brake capacity curve and conversely a reduction in brake capacity will reduce the pressure and less fluid will pass through the orifice to sump to increase the brake capacity. This autoregulation stabilizes the system. As the valve 171 is moved upwardly toward the brake off position, a greater area of the slot 202 is exposed to increase the orifice size and more fluid is exhausted to reduce the brake capacity to follow a similar lower partial brake capacity curve and conversely moving the valve toward the brake full on position decreases the orilice size to provide a similar but higher partial brake capacity curve.

During partial brake capacity operation with the valve 1711 partially open providing a brake capacity varying with speed as shown, for example, by the partial brake capacity curve, the brake capacity is limited at the value indicated by the at portion 96 of the maximum brake capacity curve. Thus at speed Z where the partial brake capacity curve intersects the portion 96 of the maximum brake capacity curve, the torque limiting valve 211 opens to release lluid from the brake circuit to further evacuate the brake chamber to limit the capacity to the value indicated by the flat portion 96 of the maximum capacity curve.

This loop control circuit employing a reciprocating valve 170 connects the brake outlet flow through line 176, valve 170, line 18'1, cooler 182, line 192, port 191, bore 172, port 186, line 187 and passage 77 to the brake chamber 40. The brake relief llow through the bleed passage 207, orifice port 201 and line 203, to sump may be partially or fully blocked by land c of valve member 171 at port 201 to partially or fully apply the bra'ke. The return llow at port 186 is always open when the brake is partially or fully applied and closed in brake ol'r position. The pressure in chamber 208 which rellects the brake outlet pressure acts on valve 171 to provide feed and on valve 211 to automatically limit the brake capacity to a safe value at high speeds. The converter tlow, after passing through the converter mixes with the brake outlet llow between lands 17111 and b and tlows to the cooler and regulator valve 194 which regulates the brake pressure in the full brake range `and the converter pressure at all speeds when the valve is in the brake on position and passes directly to the cooler and valve 194 which also regulates the converter pressure when the valve 170 is in the brake ofi position. The cooler outlet flow `returns to brake chamber with the valve 170 in the brake on position and flows through valve 194 to sump 150 with the valve 170 in the brake olf position.

In both systems the converter fluid ows through the cooler and a regulator valve to regulate converter pressure when the brake is off, but when the brake is applied the converter exhaust supplies the brake and a valve automatically controls maximum brake capacity by keeping the brake chamber full and limiting the pressure.

The brake capacity is further controlled by by-passing uid from the loop circuit by a manually controlled variable orice valve to provide partial braking and a limiting valve to limit maximum capacity to a safe value at high speeds. A control system of this type is stable so that a certain valve opening or orifice size in a given position will always provide a certain brake capacity at each speed as indicated by the curves in FIG. 2. Since the valves may be located in any position in or adjacent the transmission, it -will rbe appreicated that we have employed terms like top and bottom merely to facilitate vreference to the drawings.

If the regulator valves 82 or y19'4 are set to relieve at a pressure higher than the pressure at which the torque limiter valves 79 or 211 relieve minus the pressure drop inV coolers 66 or 182 in order to provide a higher converter pressure, the pressure in the bralce chamber will be relieved by the torque limiter valves 79 and 211 in the full brake range at the same pressure which these valves relieve to provide the limited brake range indicated by `the portion 96 of the maximum brake capacity curve.

Under these conditions in the `full brake range part of the pressure will be due to the centrifugal head of the brake and part due to a positive charging pressure from pump 53. Since the pressure generated by the brake is lo'w in this range only the excess pressure and fluid due to pump 53 will be relieved by the torque limiter valves and the brake chamber will be kept full.

Though several embodiments of the invention have been disclosed, it 'will be apparent to those skilled in the Iart that modifications may be made within the scope of the invention defined by the claims.

We claim:

l. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, brake means in said chamber` pumping uid from said inlet to said outlet and providing fluid under pressure in said outlet, a liquid sump open to atmosphere, a source lof liquid under pressure having an inlet connected to receive liquid from said sump, a second source of scavenging air under pressure, means including valve mechanism having a brake on position connecting said brake outlet and said source in a closed iiuid circuit capable of confining pressure to said brake inlet and having a brake off position connecting said brake outlet to said sump, closing said brake inlet and connecting said second source to said brake chamber to supply scavenging air to said -brake chamber.

2. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, brake means within said chamber :pumping fluid from said inlet to said outlet and providing outlet to said sump in the brake on position and to connect said brake outlet for exhaust flow to said sump in -the brake off position, second valve means operatively associated with said conduit means between said cooler and lsaid 4brake inlet to close said conduit means between said cooler and said brake inlet to prevent -flow to said brake inlet and permit exhaust ow to said sump in the brake off position and to connect said cooler to said brake inlet in said brake on position and prevent exhaust ilow to said sump, and a fluid supply connected to said conduit means Y between said rst and second valve means.

`3. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, brake means within said chamber pumping fluid from said inlet to said outlet and providing iiuid under pressure in said outlet, a sump, closed cona duit means connecting said outlet to said inlet, a cooler tion and open to connect said brake outlet and conduit i' means to said sump in the brake olii' position, second valve means operatively associated with said conduit means between said cooler and said brake inlet to close said conduit means between said cooler and said brake inlet to prevent flow to said brake -inlet and permit flow to said in the brake off position and to connect said cooler to said brake inlet in said brake on position, a liuid sup- `ply connected to said conduit means between said first and second valve means, and said conduit means Y having a third valve means limiting pressure in said brake chamber to a predetermined value.

4. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, brake means within said chamber pumping liuid from said inlet to said outlet, a sump, closed loop conduit means providing a pressure confining conduit connecting said outlet to said inlet, a cooler in Vsaid conduit means, a iirst by-pass conduit connected to said loop conduit between said outlet and said cooler to connect said loop conduit to said sump, first valve means in said ylirst by-pass conduit means to close said brake outlet connection to sump in the brake on position and to connect said ybrake outlet to said sump in the brake ol position, second valve means operatively associated with said loop conduit means between said cooler and said brake inlet to close said loop conduit means in the brake olf position and to connect said cooler to said brake inlet in said brake on position, a uid supply connected to said conduit means between said first and second valve means, a second by-pass connected to said loop conduit between said fluid supply connection and said second valve and connecting said loop conduit to said sump, and a pressure relief valve in said second by-pass permitting flow `when pressure is increased by closing said second valve in thebrake oft` position.

5. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, brake means within said chamber pumping fluid from said inlet to said outlet, a sump, closed loop conduit means providing a pressure confining conduit `connecting said outlet to said inlet, a cooler in said' conduit means, a first by-pass conduit connected to said 'loop conduit between said outlet and said cooler to connect said loop conduit to said sump, first valve means in said rst by-pass conduit to close said brake outlet connection vto sump in the brake on position and to connect said brake outlet to said sump in the brake oftposition, a second valve means in said loop conduit means between said cooler and said brake inlet to close said loop conduit means inthe brake off position and to connect said cooler to said brake inlet in said brake on position, a uid supply connected to said conduit means between said irst and second Valve means, a second by-pass connected to said loop conduit between said iiuid supply connection and said second valve and connecting said loop circuit to said sump, a rst pressure relief valve in said second bypass permitting ow when pressure is increased by closing said second valve in the brake off position, and a third .by-pass connected to said loop conduit between said outlet and said cooler, and a second pressure relief valve in said third by-pass.

K 6. The invention defined in claim 5 and said rst and second pressure relief valves employing a common spring to resiliently hold the valves in closed position.

7. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, brake means within said chamber pumping lluid from said inlet to said outlet, a sump, closed loop conduit means providing a pressure coniining conduit connecting said outlet to said inlet, a cooler Iin said conduit means, a rst by-pass conduit connected to said loop conduit between said outlet and said cooler to connect said loop conduit -to said sump, first valve means in said first by-pass conduit means between said brake outlet and said sump to close said brake outlet connection to sump in the brake on position and to connect said brake outlet to said sump in the brake off position, a second valve means in said loop conduit means between said cooler and said brake inlet to close said loop conduit means in the brake off position and to conrnect said cooler to said brake inlet in said brake on position, a uid supply connected to said conduit means be- `tweenvsaid first valve means and said cooler, a second by-pass connected to said loop conduit between said fluid supply connection and said second valve and connecting said loop circuit to said sump, and a pressure relief valve in said second by-pass permitting ilow when 11 pressure is increased by closing said second valve in the brake-olf position.

8. The invention defined in claim 7 and a scavenging air supply of air under pressure, and scavenging valve means supplying air to said chamber when said first and second valve means are in the brake oi position.

9. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, brake means within said chamber pumping fluid from said inlet to said outlet, a sump, closed loop conduit means providing a pressure confining conduit connecting said outlet to said inlet, a cooler iu said conduit means, a first bypass conduit connected to said loop conduit between said outlet and said cooler to connect said loop conduit to said sump, first valve means in said first by-pass conduit means to close said brake outlet connection to sump in the brake on position and to connect said brake outlet to said sump in the brake off position and to automatically connect said loop conduit to said sump in response to excessive pressure in said loop conduit, a second valve means in said loop conduit means between said cooler and said brake inlet to close said loop conduit means in the brake oli position and to connect said cooler to said brake inlet in said brake on position, a fluid supply connected to said conduit means between said rst and second valve means, a second by-pass connected to said loop conduit between said fiuid supply connection and said second valve and connecting said loop circuit to said sump, and a pressure relief valve in said second by-pass permitting flow when pressure is increased by closing said second valve in the brake-olf position.

l0. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, hydrodynamic brake means in said brake chamber operative during braking to pump fluid from said inlet to said outlet and delivering fiuid under pressure to said outlet, a closed hydraulic loop circuit providing a pressure fluid confining conduit connecting said outlet to said inlet in a path separate from the fluid in said brake chamber, a restriction in said loop circuit dividing said loop circuit into an inlet portion adjacent said inlet and an outlet portion adjacent said outlet, means including a source external of said loop circuit connected to said loop circuit to supply uid from said source to said loop circuit, and a controlled variable valve means operatively connected to said outlet portion to release uid from said outlet portion of said loop circuit to control the brake capacity.

11. In a hydrodynamic brake, a brake chamber having an inlet and and outlet, hydrodynamic brake means in said brake chamber operative during braking to pump uid from said inlet to said outlet and delivering uid under pressure to said outlet, a closed hydraulic loop circuit providing a pressure iiuid confining conduit connecting said outlet to said inlet in a path separate from the fiuid in said brake chamber, a restriction in said loop circuit dividing said loop circuit into an inlet portion adjacent said inlet and an outlet portion adjacent said outlet, means including a source external of said loop circuit connected to said loop circuit to supply uid from said source to said loop circuit, and said outlet portion having pressure responsive means to release fluid from said hydraulic loop circuit in response to pressure in said loop circuit to limit the brake capacity.

12. :In a hydrodynamic brake, a brake chamber having an inlet and an outlet, hydrodynamic brake means in said brake chamber operative during braking to pump fluid from said inlet to said outlet and delivering fluid under pressure to said outlet, a closed hydraulic loop circuit providing a pressure fiuid confining conduit connecting said outlet to said inlet in a path separate from the iiuid in said brake chamber, a restriction in said loop circuit dividing said loop circuit into an inlet portion adjacent said inlet and an outlet portion adjacent said outlet, means including a source external of said 4loop circuit connected to said loop circuit to supply fluid from said source to said loop circuit, said outlet portion having a variable orifice to release uid from said loop circuit to provide partial braking, said outlet portion having pressure responsive means to release uid from said hydraulic loop circuit in response to pressure in said loop circuit to limit the maximum brake capacity, and said inlet portion having pressure responsive means to relieve pressure therefrom when the brake chamber is full to limit brake capacity and pressure in the chamber when the brake chamber is full.

13. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, hydrodynamic brake means in said brake chamber operative during braking to pump fluid from said inlet to said outlet and delivering fluid under pressure to said outlet, a closed hydraulic loop circuit providing a pressure iluid confining conduit connecting said outlet to said inlet in a path separate from the fluid in said brake chamber, a restriction in said loop circuit dividing said loop circuit into an inlet portion adjacent said inlet and an outlet portion adjacent said outlet, fiuid supply means including a source external of said loop circuit providing a volume of fluid which is substantially constant at any given brake speed from said source and connected to said loop circuit to supply said volume of fluid from said source to said loop circuit, and said outlet portion having a variable orifice to release fluid from said closed loop circuit to provide partial braking.

14. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, hydrodynamic brake means in said brake chamber operative during braking to pump uid from said inlet to said outlet and delivering uid under pressure to said outlet, a closed hydraulic loop circuit providing a pressure fluid confining conduit connecting said outlet to said inlet in a path separate from the fluid in said brake chamber, a restriction in said loop circuit dividing said loop circuit into an inlet portion adjacent said inlet and an outlet portion adjacent said outlet, fluid supply means including a source external of said loop circuit providing a volume of fluid which is substantially constant at any given brake speed from said source and connected to said loop circuit to supply said volume of fluid from said source to said loop circuit, and said outlet portion having pressure responsive means to release uid from said hydraulic loop circuit in response to pressure in said loop circuit to limit the brake capacity.

15. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, hydrodynamic brake means in said brake chamber operative during braking to pump fluid from said inlet to said outlet and delivering fluid under pressure to said outlet, a closed hydraulic loop circuit providing a pressure fluid confining conduit connecting said outlet to said inlet in a path separate from the fluid in said brake chamber, a restriction in said loop circuit dividing said loop circuit into an inlet portion adjacent said inlet and an outlet portion adjacent said outlet, uid supply means including a source external of said loop circuit providing a volume of fluid which is substantially constant at any given brake speed from said source and connected to said loop circuit to supply said volume of fluid from said source to said loop circuit, and said inlet portion having pressure responsive means to relieve pressure when the brake chamber is full to limit brake capacity.

16. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, hydrodynamic brake means in said brake chamber operative during braking to pump fluid from said inlet to said outlet and delivering iiuid under pressure to said outlet, a closed hydraulic loop circuit providing a pressure iiuid confining conduit connecting said outlet to said inlet in a path separate from the fluid in said brake chamber, a restriction in said loop circuit dividing the loop circuit into an inlet portion adjacent said inlet and an outlet portion adjacent said outlet, means including a source external of said loop circuit to supply a volume of fluid which is substantially con- 13 stant at any given brake speed from said source and connected to said loop circuit to supply said volume of fluid from said source to said loop circuit, said outlet portion having va variable orifice valve means closing said orifice in the brake full on position to prevent release of iiuid from said loop circuit and fully opening said valve means in the brake oft position to drain the loop circuit and partially opening said valve means in intermediate positions to partially release iluid from said loop circuit to provide partial braking, said inlet yportion having brake inlet valve means having a brake on position permitting llow to said brake chamber and a brake orf position blocking ilow to said brake chamber and a pressure relief valve in said outlet portion between said restriction and said brake inlet valve means to relieve pressure when the brake chamber is full to limit brake capacity and pressure in the chamber when the brake chamber is full.

17. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, a continuous conduit connecting said outlet to said inlet and conlining fluid under superatmospheric pressure throughout its length between said outlet to said inlet, hydrodynamic rotor means in said chamber pumping a quantity of fluid from said inlet through said brake chamber to said outlet and through said continuous conduit to said inlet, duid supply means connected at a supply point to said conduit supplying uid to be added to the quantity of fluid flow provided by said 4hydrodynamic rotor means and control means operatively associated with said conduit and actuated by a single manual control having a full brake-on and a brake-oli position and in the brake-on position providi-ng free ow through said conduit and releasing a controlled quantity of duid from said conduit, and in said brake-olf position blocking llow at a blocking point in said conduit between said point of supply and inlet and releasing uid Ifrom said conduit at a release point between said outlet and said blocking point.

18. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, a continuous conduit connecting said outlet to said inlet and coniining uid under superatmospheric pressure throughout its length between said outlet to said inlet, hydrodynamic rotor means in said chamber pumping a quantity of iluid from said inlet through said brake chamber to said outlet and through said continuous conduit to said inlet and providing an outlet pressure proportional to the torque absorbed by the brake, fluid supply means connected at a supply point to said conduit continuously supplying during brake operation a predetermined controlled quantity :llow of iluid to be added to the quantity of fluid flow provided by said hydrodynamic rotor means and control means operatively associated with said conduit and actuated by a single manual control having a full brake-on, a partial brake-on and a brake-off position and in the brake-on position providing' free flow through said conduit and releasing a controlled quantity of fluid from said conduit, and in partial brake-on position providing free flow through said conduit and releasing a reduced quantity of uid from said conduit and in said brake-off position blocking flow at a blocking point in said conduit between said point of supply and inlet and releasing uid from said conduit at a release point between said outlet and said blocking point.

19. ln a hydrodynamic brake, a brake chamber having an inlet rand an outlet, a continuous conduit connecting said outlet to said inlet and coniining iluid under superatmospheric pressure throughout its length from said outlet to said inlet, hydrodynamic rotor means in said chamber pumping a quantity of fluid from said inlet through said brake chamber to said outlet and through said continuous conduit to said inlet `and providing an outlet pressure proportional to the torque absorbed by the brake, uid supply means connected to said conduit continuously supplying during brake operation a predetermined controlled quantity ilow of fluid per unit of time to said conduit to be added to the quantity of lluid ilow provided by said hydrodynamic rotor means and control means connected to said conduit and opera-tive to release a controlled quantity ow of iluid per unit of time from said conduit normally equal to the quantity of iluid supplied to said conduit by said uid supply means under a predetermined outlet pressure to provide a predetermined torque absorbed by the brake and responsive to an increase in pressure due to an increase in the torque absorbed by the brake to increase the release of fluid to decrease the torque absorbed and responsive to a decrease in pressure due to a decrease in the torque absorbed to decrease the release of fluid to increase the torque absorbed.

20. In a hydrodynamic brake, a brake chamber having an inlet land an outlet, a continuous conduit connecting said outlet to said inlet and confining fluid under superatmospheric pressure throughout its length between said outlet to said inlet, hydrodynamic rotor means in said chamber pumping during brake operation a quantity of fluid from said inlet through said brake chamber to said outlet and through said continuous conduit to said inlet and providing an outlet pressure proportional to the torque absorbed by the brake, uid supply means connected to said conduit continuously supplying during brake operation a substantially constant quantity ilow of uid per unit of time `at each brake rotor means speed to said conduit to be added to the quantity of lluid flow provided by said hydrodynamic rotor means and control means connected to said conduit and operative in each of a plurality of positions to release a normally constant quantity ow of lluid per unit of time from said conduit normally equal to the quantity of iiuid supplied to said conduit by said fluid supply means under a predetermined outlet pressure to provide a predetermined torque absorbed by the brake in each of said plurality of positions and operative in each position in response to an increase in pressure due to an increase in the torque absorbed by the brake to increase the release of uid to decrease the torque absorbed and also operative in each position in response to -a decrease in pressure due to a decrease in the torque absorbed to decrease the release of fluid to increase the torque absorbed.

2l. In a hydrodynamic brake, a brake chamber having an inlet and an outlet, hydrodynamic brake means in said brake chamber operative during braking to pump iluid from said inlet to said outlet and delivering lluid under a pressure head lto said outlet proportional to brake capacity and brake speed, a closed hydraulic loop circuit connecting said brake chamber outlet to said brake chamber inlet in a path separate from the fluid in said brake chamber providing a pressure fluid coniining conduit throughout its length from said brake chamber outlet to said brake chamber inlet, means including a source external of said loop circuit and brake chamber providing a volume of iluid per unit of time which is substantially constant at any given brake speed from said source and connected to said loop circuit to supply said volume of fluid from said source to said loop circuit and control means connected -to said loop circuit to release said volume of iluid from said loop circuit at a predetermined pressure head to provide a predetermined brake capacity at each brake speed and automatically operative in response to an increase in pressure head to release an increased volume of ilow from said loop circuit to decrease the pressure head and responsive to a decrease in pressure head -to release a decreased volume of flow from said loop circuit to increase the pressure head to automatically maintain said predetermined pressure head and brake capacity.

22. The invention dened in claim 21 and said control means being adjust-able to release said volume of fluid from said loop circuit in each of a plurality of positions at each of a plurality of predetermined pressure heads to provide each of a plurality of predetermined brake capacities.

23. The invention deiined in claim 21 and said control including a bypass conduit connected to said loop circuit and an oriiice in said bypass conduit to control the release of said iluid from said loop circuit through said bypass conduit.

24. The invention defined in claim 21 and said control including pressure regulating valve means operative to regulate the pressure in said loop circuit at a predetermined value to control the release of said iluid from said loop circuit.

25. The invention defined in claim 21 and a check valve in said loop circuit between said outlet and the connection of said source to said loop circuit.

26. The invention defined in claim 21 and said control means having a brake-on and a brake-olf position and including a manually controlled variable orifice valve operable to vary the oriiice to vary the brake capacity in said brake-on position and to prevent the supply of liuid from said loop circuit Ithrough said brake inlet to said brake chamber and exhaust said loop circuit in said brake-off position.

27. The invention defined in claim 21 and said loop circuit having a restriction to provide a pressure drop, said control means having a brake-on and a brake-olf position and being connected to said loop circuit between said outlet and said restriction and a brake shut-olf valve operatively associated with said loop circuit between said restriction and said brake inlet to permit ow through said loop circuit to said brake inlet in said brakeon position and -to exhaust 1said loop circuit in said brakeoff position.

28. The invention defined in claim 21 and means to vent said brake chamber to atmosphere during brake operation and to supply air under pressure to said brake chamber when the brake is disengaged to assist scavenging said brake chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,915,547 North et al. June 27, 1933 1,985,889 Mater et al. Jan. 1, 1935 2,170,128 Mater Aug. 22, 1939 2,232,252 Mathey Feb. 18, 1941 2,498,572 OLeary Feb. 21, 1950 2,634,830 Cline Apr. 14, 1953 2,715,876 Schneider Aug. 23, 1955 2,716,339 Cline Aug. 30, 1955 2,827,989 Christensen Mar. 25, 1958 2,864,473 Christensen et al Dec. 16, 1958 2,889,013 Schneider June 2, 1959 

